we have never been refused a spot because of our size and prior to this we had a 35' Class A. We looked at downsizing and decided we didn't want to give up the living space. Our only problem is getting up the steps since we both have problems with steps.

There is no BEST size for an RV. Here is a link to a website that will tell you the size RV's that can fit into spaces at any state or federal campground. Campground reservations
Obviously a smaller coach will be more maneuverable and allow you more places to chose from to park but you may find the size too cramped for long term comfort.
The large coaches certainly provide more living space, but they are more difficult to maneuver into any tight areas such as some fueling stations and the roads in some campgrounds. They also may be a little more difficult to park at your home base.
You need to review your own RVing needs and make your decision based on your own criteria. What works for some people may not work for you at all.

We don't look at state parks anymore - just too much trouble trying to get reservations (everyone in the state will make reservations in January for the whole summer and then not cancel, they just don't show up, so empty sites sit for the weekends) and the price at most is ridiculous if you don't have their annual pass - - most charge extra for the toad.

We do like COE parks and use them whenever we can.

If you are only going to fulltime for 2 years, then why bother with a new rig; just use what you have now.

I got tired of trying to park a 36 ft. TT with a cab 1/2 PU Truck. When I moved to a Class A, I wanted to keep the length down so that fueling and parking would be less of a pain. My 34 ft MH is a good fit for me. It has plenty of storage inside and out. I can wheel it in and out of tight spots with no trouble. With two slides it feels big to us and has plenty of room for two people.